What is your objective: To inform them? To persuade them of an opinion? To motivate them to take action? Without that, we can't help you (and, if I may be so bold, you can't give a good talk either with or without our help).

Also, consider cultural factors: are they all from a "mainstream" North American cultural background, or do you have to take different thought patterns and educational backgrounds into account?

In other words: please say more!